High fidelity loudspeaker system



u 1965 JEAN-PIERRE DUDOGNON 3,136,509

HIGH FIDELITY LOUDSPEAKER SYSTEM Filed Feb. 5, 1965 F/GI lOb

JEAN-PIERRE DUOOGNON BY 8 MSW ATTORNEY United States Patent HIGH FIDELITY LOUDSPEAKER SYSTEM Jean-Pierre Dudognon, 35 Rue de Nanterre, Asnieres, Seine, France Filed Feb. 5, 1963, Ser. No. 256,336 Claims priority, application France, Feb. 13, 1962, sszs'n, Patent 1,322,235 Claims. ((Zl. ISL-31) The present invention relates to a substantially aperiodic loudspeaker system including an acoustic chamber which provides high fidelity reproduction of sounds and it is intended chiefly, but not exclusively, for operation with a loud-speaker of the dynamic type uniformly reproducing a broad band of frequencies ranging between about 20 and 12,000 cycles.

My invention has more particularly for its object a compact apparatus of conventional shape, the adjustment of which is simple and the cost of which is low, while it operates by virtue of its novel construction over a range of frequencies which extends between extreme low notes and extreme high notes without any marked resonance or attenuation when transmitting any of said frequencies.

According to a main feature of my invention, the acoustic energy fed into the chamber by the loud-speaker is subdivided into two channels, a very short channel arranged coaxially with the generator of acoustic energy and leading to a narrow passage forming an air pocket and a second channel provided with reflectors arranged in herring-bone formation, said second channel leading to the outer end of said air pocket.

The pocket-forming passage is provided in the vicinity of the point at which it meets the second channel with adjustable ports and it terminates as an acute dihedral angle so as to prevent the formation of standing waves of a length corresponding to the length of the passage.

According to a second feature of the invention, the second channel provides, through its arrangement of reflectors in herring-bone formation, differences in the lengths of the paths followed by the sound waves according to their angles of incidence. The arrangement is such that the acoustic energy encounters less acoustic impedance traveling in the direction away from the loudspeaker diaphragm, than in the opposite direction in which the efiiciency of transmission is almost zero. This results in the elimination of standing waves.

sion ascribable to the viscosity of the air in the air pocket;

said phenomenon is increased by the fact that the cross sectional area of the first channel in a direction coaxial with the loud-speaker followed by that of the air jacket decreases gradually in a manner such that the ratio between the acoustic energy and the volume inside which said energy is restricted, increases;

By reason of the inertia of the air in the air pocket; Because the air pocket is provided with one or mor adjustable ports which allow adjusting the acoustic contrast, said ports producing a coupling between the inside and the outside of the chamber, which leads to a novel resonating system which has a tendency to oppose the resonating system already extant in the chamber.

According to my invention, said chamber provides a very high acoustic efficiency for the loud-speaker together with an excellent reproduction of any transient sound, as ascribable, in particular, to the absence of standing waves, while a very reduced level of vibrations transmitted to the battle board is obtained and it is possible to adjust the ire-echoing and acoustic contrast by modifying the the effective size of the openings of the ports which produce a coupling between the acoustic energy inside and outside the chamber.

Various other features will appear from reading the following description, reference being made to the accompanying drawings, wherein:

FIG. 1 is an elevational view of a cabinet enclosing a high fidelity acoustic reproducing system according to my invention.

FIG. 2 is a plan sectional view of the acoustic chamber taken on the line AA of FIG. 1.

FIG. 3 is a rear view of one half of the cabinet or enclosure.

FIG. 4 shows, by way of a modification, an acoustic chamber adapted to be associated with a tape recorder.

Turning to FIG. 1, the cabinet is subdivided into two parts of which the upper part 1 houses the radio receiver including the amplifier (not shown) and, optionally, a tape recorder. The lower part, 2, forms the acoustic chamber for the loudspeaker system according to my invention.

As illustrated cross-sectionally in FIG. 2, the acoustic energy transmitted by the loud-speaker 3, mounted in a bafile board 30, is distributed into two channels: a first very short channel or acoustic pasage 4, defined by first partition means 4a, 4b. The channel or passage 4 is coaxial with respect to the loudspeaker 3 and converges rearwardly, leading at 5 to a passage or air pocket 6 defined by second partition means formed by a wall 6a and the rear wall 2b of the chamber 2. The air pocket 6 has a gradually decreasing cross-section proceeding leftwardly. A second acoustic passage or channel 7, defined by third partition means formed by the baffle board 3a and a wall 6a, is provided with a system of wall members or reflectors 8 of different lengths arranged in herringbone formation, that is carried by either side or" the channel and directed inwardly and forwardly of the latter.

By reason of their arrangement and different lengths, said reflectors provide differences in the lengths of the paths of the acoustic waves according to the angle of incidence of the latter thereby detuning the second acoustic passage '7 from resonance at any particular frequency within the wide range. The arrangement is such that the acoustic energy travels with excellent efiiciency in the direction of the arrow F away from the loud-speaker diaphragm, whereas the efiiciency of transmission is almost zero in the opposite direction, which eliminates standing waves. The end of this channel 7 forms the area where the density of acoustic ener y is at a maxi e1 mum. The end 9 of the second acoustic passage 7 communicates with a triangular auxiliary channel lltta through an aperture 9a. The auxiliary channel Eda opens downwardly directly above a reflector it) located exteriorly of the chamber 2. The reflector it) is connected to the bottom wall 2a of the chamber 2 by a hinge 1%. The hinge Zltib permits angular displacement of the reflector it) about a horizontal axis located near and extending parallel to the rear wall 21) of the chamber 2. The hinge 1% is provided with a locking knob 100 for locking the reflector lit) in any desired position of angular adjustment. The hinge 10b and reflector lltl permit adjustment of the acoustic coupling between the inside and the outside of the chamber 2.

The ends and 9 of the channels opening into the air pocket or passage 6 are spaced as far away as possible from each other. The air pocket 6 is provided with ports Itll which are adjustable through the agency of a perforated sliding plate 12 (FIG. 3) and it terminates as an acute dihedral angle at 5 (FIG. 2), whereby no standing wave of a length corresponding to its length can be produced. The arrangement is associated with independent tweeter means 13 for the reproduction of high notes.

The chamber described allows damping the rcarwardly directed waves since the waves passing out of the channels 4 and 7 enter the air pocket 6 from opposite directions and show phase differences which vary by reason of the actual progression of waves over the herring-bone reflector structure in the channel '7. Furthermore, there is a damping obtained through the direct dissipation due to the viscosity of the air in the air pocket and to its inertia. The correct reproduction of transient sound is associated directly with the efficiency of said damping.

My improved chamber allows furthermore obtaining the return of the energy originally transmitted inside the baflle board to be partly returned to the loud-speaker diaphragm in phase with the latter through the channel 4. This is a phenomenon of diffuse resonance which is obtained for all the frequencies to be transmitted; the efiiciency of the loud-speaker is thus considerably increased.

Inside the air pocket, the sound passing out of the channel '7 forms, by reason of the successive reflections to which it is subjected, which reflections lead to different delays, a series of vibratory nodes and loops which have a tendency to constitute a coherent system with the sound passing out of the channel 4, which leads to the phenomenon of diffuse resonance. The fraction of energy dissipated corresponds to the component of the waves which are in phase opposition inside said air pocket, which forms a cause of damping of the rearwardly directed waves.

The waves travel over different paths in the channel 7. For a number of said paths, there is a more or less perfect phase coincidence with the waves passing out of the channel 4 and for other paths, there is an opposition in phase and a dissipation of energy. A fraction of the acoustic energy radiated inside the chamber constitutes thus a resonating system, in phase with the loud-speaker diaphragm. For each period, almost one half of said energy is consequently returned to the outside of the chamber by the diaphragm; said phenomenon is very important from a quantitative standpoint, although the energy associated with each cycle of resonance is very unimportant.

The rectilinear shape of the curve of response, as a function of frequency, is thus obtained, not by cutting out the high note resonances by means of a damping material inside the chamber or the like, but through an effect of diflFuse or blurred resonance for all the frequencies transmitted.

According to my invention, the resonant systems in the type of chamber considered are immediately cut out upon input of a transient wave by reason:

Of the comparatively very low amount of acoustic energy in the resonant system;

Of the critical damping value;

Of the fact that the transient waves do not reach simultaneously both ends of the air pocket, which produces thus immediately in said air jacket dilferent oscillatory combinations. For each transient wave, the damping coefficient of the chamber increases consequently until a further ditfuse resonant system is obtained. The increase of the damping factor is ascribable to the consumption of energy required for neutralizing the actual wave system and producing a further system.

By way of a modification, FIG. 4 illustrates anacoustic chamber adapted to equip an acoustic reproduccr including a loud-speaker t4 the acoustic energy of which is distributed into two channels: a coaxial channel 15 leading to a passage reforming an air pocket provided with one or more adjustable ports 17, and a channel 18 associated with a set of reflectors 19 leading to the end 29 of the passage 16. The operation of said chamber is identical with that of the chamber serving for high fidelity reproduction.

Obviously, many modifications may be made in the examples described and illustrated as concerns both the shape and the arrangement of the different components of the chamber without thereby unduly widening the scope of the invention as defined in the accompanying claims.

In brief, I obtain an excellent transmission of the sounds passing out of the loudspeaker without any resonance or marked fading throughout the range of frequencies to be considered and the acoustic yield of the loud-speaker is very high and ensures a minimum distortion under optimum listening conditions. Transient sounds are also reproduced faithfully. No noise is introduced by reason of the absence of standing waves and, lastly, the vibrations transmitted to the baflie board are reduced to a minimum as a consequence of the damping of the return waves.

What I claim is:

1. A substantially aperiodic loudspeaker system comprising, in combination: means including bafl le board means defining an acoustic chamber, said bafiie board means extending transversely of said chamber at the front thereof; a rearwardly extending dynamic speaker mounted in said baflle board means; first partition means in said chamber defining a first rearwardly convergent acoustic passage efiectively coaxial with said speaker; second partition means defining an air pocket in said chamber extending adjacent to the rear of said chamber substantially throughout the entire width thereof, said first acoustic passage communicating directly with said air pocket at a location adjacent to one side of said chamber; third partition means defining a second acoustic passage extending laterally away from said speaker and communicating directly with said air pocket at a location adjacent to the other side of said chamber, said third partition means including a plurality of wall members of differing lengths which extend from the sides of said second passage at spaced locations therealong obliquely toward the longitudinal axis thereof and convergently away from said speaker whereby the acoustic impedance of said second passage is less for acoustic Waves traveling away from said speaker than in the opposite direction, said differing lengths detuning said second passage from resonance at any particular frequency within a predetermined range of frequencies; and angularly adjustable reflector means located ex-teriorly of said cabinet, said reflector means communicating with the interior of said cabinet in proximity to the location where said second passage communicates with said air pocket.

2. A system according to claim 1, wherein said second acoustic passage is at least four times longer than said first passage.

3. A system according to claim 1, wherein said air pocket is convergent from said one side of said chamber References Cited by the Examiner toward said other side thereof. I P m NT 4. A system according to claim 1, in which said air UN TED STATES ALE S pocket communicates with the exterior of said chamber at 2,805,729 9/57 Read a. location adjacent to said other side thereof. 5 3 047O9O 7/62 Pruden Isl-"31 5. A system according to claim 4 wherein said air pocket communicates with the exterior of said chamber FOREIGN PATENTS through at least one aperture, said system further com- 356,557 2/38 Italy.

prising adjustable means for varying the effective size of said aperture. 10 LEO SMILOW, Primary Examiner. 

1. A SUBSTANTIALLY APERIODIC LOUDSPEAKER SYSTEM COMPRISING, IN COMBINATION: MEANS INCLUDING BAFFLE BOARD MEANS DEFINING AN ACOUSTIC CHAMBER, SAID BAFFLE BOARD MEANS EXTENDING TRANSVERSELY OF SAID CHAMBER AT THE FRONT THEREOF; A REARWARDLY EXTENDING DYNAMIC SPEAKER MOUNTED IN SAID BAFFLE BOARD MEANS, FIRST PARTITION MEANS IN SAID CHAMBER DEFINING A FIRST REARWARDLY CONVERGENT ACOUSTIC PASSAGE EFFECTIVELY COAXIAL WITH SAID SPEAKER; SECOND PARTITION MEANS DEFINING AN AIR POCKET IN SAID CHAMBER EXTENDING ADJACENT TO THE REAR OF SAID CHAMBER SUBSTANTIALLY THROUGHOUT THE ENTIRE WIDTH THEREOF, SAID FIRST ACOUSTIC PASSAGE COMMUNICATING DIRECTLY WITH SAID AIR POCKET AT A LOCATION ADJACENT TO ONE SIDE OF SAID CHAMBER; THIRD PARTITION MEANS DEFINING A SECOND ACOUSTIC PASSAGE EXTENDING LATERALLY AWAY FROM SAID SPEAKER AND COMMUNICATING DIRECTLY WITH SAID AIR POCKET AT A LOCATION ADJACENT TO THE OTHER SIDE OF SAID CHAMBER, SAID THIRD PARTITION MEANS INCLUDING A PLURALITY OF WALL MEMBERS OF DIFFERING LENGTHS WHICH EXTEND FROM THE SIDES OF SAID SECOND PASSAGE AT SPACED LOCATIONS THEREALONG OBLIQUELY TOWARD THE LONGITUDINAL AXIS THEREOF AND CONVERGENTLY AWAY FROM SAID SPEAKER WHEREBY THE ACOUSTIC IMPEDANCE OF SAID SECOND PASSAGE IS LESS FOR ACOUSTIC WAVES TRAVELING AWAY FROM SAID SPEAKER THAN IN THE OPPOSITE DIRECTION, SAID DIFFERING LENGTHS DETUNING SAID SECOND PASSAGE FROM RESONANCE AT ANY PARTICULAR FREQUENCY WITHIN A PREDETERMINED RANGE OF FREQUENCIES; AN ANGULARLY ADJUSTABLE REFLECTOR MEANS LOCATED EXTERIORLY OF SAID CABINET, SAID REFLECTOR MEANS COMMUNICATING WITH THE INTERIOR OF SAID CABINET IN PROXIMITY TO THE LOCATION WHERE SAID SECOND PASSAGE COMMUNICATES WITH SAID AIR POCKET. 